Streamlet: An Absurdly Simple, Textbook Blockchain Protocol

Numerous works in the past have focused on constructing simple and understandable distributed consensus protocols. In this talk, I will present an absurdly simple consensus protocol called Streamlet. The entire protocol is: every epoch, a leader proposes a block extending the longest chain it has seen so far. Everyone votes for (i.e., signs) the first block proposed by the leader if it extends from one of the longest notarized chains they have seen so far. When a block collects votes from 2/3 of the nodes, it becomes notarized. Notarized does not mean final. Finality is decided with the following rule: for any chain in which all blocks are notarized and moreover, the last three blocks have consecutive epoch numbers, the entire chain except the first block is final. Streamlet is inspired by the community's past five years of work on consensus motivated by decentralized blockchains. To the best of our knowledge, it is the simplest embodiment known thus far, and it subsumes classical landmark protocols such as PBFT/Paxos and their numerous variants. It is a great fit for pedagogy. Streamlet has been incorporated into courses at universities such as Stanford and CMU. Streamlet is also part of my new distributed consensus textbook available at http://distributedconsensus.net/

This is joint work with Benjamin Chan.